TITLE: Thurston geometries in dimension 4
QUESTION [15 upvotes]: In the sense of W. Thurston here, there is 3 geometries in dimension 2  and there is 8 geometries in dimension 3. 
Question: How many different geometries (in the sense of Thurston) do we have in dimension 4 ?

REPLY [22 votes]: The 4-dimensional geometries were classified in the unpublished thesis of Filipkiewicz, which is available here.